Donald Trump's odds down to 12-1 to win 2016 election

Donald Trump once had 100-1 odds to win the 2016 U.S. presidential election. Now, he's 12-1 at some books. Getty

Donald Trump has the international betting market's attention, but despite what some polls suggest, oddsmakers have the boisterous billionaire pegged as a second-tier underdog to be the next president of the United States.

Heading into Wednesday's Republican debate, Trump is listed as low as 12-1 to win the 2016 election. Just six weeks ago, he was sitting at 100-1 at sports books in the United Kingdom. At William Hill, he's gone from 50-1 to 7-1 to win the Republican nomination.

Trump's rise has been brisk and loud, but he still has a long ways to go to catch consensus favorite Hillary Clinton, who is currently even money to be the next president. More money has been bet on Clinton than any other candidate -- 10 times more than Trump at Ladbrokes, according to head of political odds Matthew Shaddick.

William Hill reported taking bets on Clinton to one day become president as far back as the 1990s, when her husband, Bill, was in the White House.

Republican Jeb Bush, at 7-2, is the second favorite, followed by Wisconsin Gov. Scott Walker (10-1). U.S. Sen. Bernie Sanders of Vermont and Trump are next at 12-1. A bettor in 2014 at Ladbrokes backed Sanders at 500-1 and would win more than £75,000 with an upset victory.

It's very early in the campaign, and a lot could change. Shaddick, at Labrokes, estimates only 5 percent of the total money that will be wagered on the presidential election has been placed. But plenty more is on the way. A record £1.5 million ($2.3 million) was bet on the 2012 U.S. election, won by Barack Obama, at William Hill.

"Interest in Trump has enhanced the contest as a whole, but it's very early," William Hill media relations director Graham Sharpe told ESPN Chalk in an email. "This could well end up being our biggest-ever political betting market, an honor currently held by betting on the Scottish Independence Referendum."

Trump is the third choice, behind Bush and Walker, to be the Republican nominee at U.K. betting exchange BetFair, a peer-to-peer market where candidates are traded like stocks. Trump was trading at 6-1 to win the Republican nomination this week. He was once listed at 339-1 in the presidential race at BetFair.

U.S. Sen. Marco Rubio of Florida is also in the Republican mix. Rubio attracted the largest single bet at William Hill to this point: £4,000 from a London-based punter at 12-1.

Nevada sports books are prohibited from offering betting on federal elections. A 2014 Nevada bill aimed at legalizing betting on elections died in committee.

Jay Kornegay, vice president of the Westgate Las Vegas SuperBook, and longtime Nevada bookmaker Jimmy Vaccaro believe betting on the presidential election would be one of the largest market the books offer, comparable to the Super Bowl.

"It would be wall-to-wall people," Vaccaro told ABC News in May. "It would be something like we saw this past week for the [Floyd] Mayweather [versus Manny Pacquiao] fight."

Nearly $116 million was bet on this past Super Bowl between the Seattle Seahawks and New England Patriots at Nevada sports books.